A number of experiments have been performed in an effort to better understand the photoinitiated chain decomposition of ClN3. Discharge-flow methods were used to determine the rate of energy exchange between vibrationally excited N-2 (a likely chain carrier) and ClN3 The rate constant for energy transfer from N-2(v=1) to ClN3 was found to be (2.0 +/- 1.0) x 10(-13) cm(3) s(-1) at 300 K. This process is thought to excite the v(2) mode in ClN3 with the release of 281 cm(-1) of excess energy. Experiments were also performed in which the decomposition of ClN3 was initiated by photolysis with a pulsed KrF laser at 249 nm, with subsequent observation of the time dependence of the densities of ClN3, electronically excited NCl(a(1)Delta), and vibrationally excited ClN3(v(2)) A kinetic model for the ClN3 decomposition was assembled based on reactions with NCl-(a(1)Delta) and N-2(v).